1. Field of the Invention
The present invention relates to combination locks. More specifically, the invention relates to a combination lock which provides increased manipulation resistance.
2. Related Art
It is common in combination locks, such as that disclosed in the U.S. Pat. No. 4,756,176, which is herein incorporated by reference, to provide a fence lever control device which includes means for normally keeping the nose of the fence lever spaced from the drive cam and only moving the fence lever and its associated nose toward the drive cam when tumbler wheel gates are aligned with one another and are ready to receive the fence member of the fence lever as part of the authorized opening of the lock. These prior art means for keeping the nose of the fence lever spaced from the drive cam were developed in order to prevent a lock manipulator from determining where the drive cam gate is and then manipulating the lock parts in a predetermined manner to bring the fence member in contact with edges of the gates of the wheel assemblies while the lever nose is positioned in the drive cam gate. However, such prior known mechanisms have been fairly complicated to manufacture and are not well adapted to ease of assembly techniques in mass production of combination locks.
U.S. Pat. No. 47,575 to Sargent et al. and U.S. Pat. No. 57,574 to Sargent et al. disclose locks which use a magnet to attract a dog into engagement with notches in permutation wheels when retraction of a bolt is enabled. These locks require a complex apparatus including an armature for activating and deactivating the magnet. The dog is a separate member from a swing-gate that is connected to the bolt and enables retraction of the bolt.